ENHANCED OSTEOCONDUCTION AND DEFECT FILLING ASSOCIATED WITH ALENDRONATE COATED POROUS TANTALUM

Abstract

Introduction: Achieving durable implant–host bone fixation is the major challenge in uncemented revision hip arthroplasty when significant bone stock deficiencies are encountered. The purpose of this study was

1. to develop an experimental model which would simulate the clinical revision hip scenario and

2. determine the effects of alendronate coating on porous tantalum on gap filling and bone ingrowth in the experimental model.

Methods: Thirty-six porous tantalum plugs were implanted into the distal femur, bilaterally of 18 rabbits for four weeks. There were 3 groups of plugs inserted; control groups of porous tantalum plugs (Ta) with no coating, a 2nd control group of porous tantalum plugs with micro-porous calcium phosphate coating, (Ta-CaP) and porous tantalum plugs coated with alendronate (Ta-CaP-ALN). Subcutaneous fluorochrome labelling was used to track new bone formation. Bone formation was analysed by backscattered electron microscopy and fluorescence microscopy on undecalcified histological sections.

Results: The relative increase in mean volume of gap filling, bone ingrowth and total bone formation was 124 %, 232 % and 170 % respectively in Ta-CaP-ALN compared with the uncoated porous tantalum (Ta) controls, which was statistically significant. The contact length of new bone formation on porous tantalum implants in Ta-CaP-ALN was increased by 700% (8-fold) on average compared with the uncoated porous tantalum (Ta) controls.

Discussion: Alendronate coated porous tantalum significantly modulated implant bioactivity compared with controls. This study has demonstrated the significant enhancement of bone-implant gap filling and bone ingrowth, which can be achieved by coating porous tantalum with alendronate. It is proposed that, when faced with the clinical problem of revision joint replacement in the face of bone loss, the addition of alendronate as a surface coating would enhance biological fixation of the implant and promote the healing of bone defects.